The
first post of this link shows where GaryKD installed his fan on his Dometic fridge.
He found no fans on his fridge as the Norcold has.
Its also advisable to check the rear vent area of fridge and see if you have a clear path up through vent area and out the roof vent sometimes a baffle or insulation will slip off top of fridge and block the upper vent area.
You may not have a baffle as required by fridge mfg installed per their insulation spec's.
There is 12v in rear area of fridge for fan and you can use thermal switch or just leave fan on all the time fridge is on.
Some people have installed fans on cooling fins inside box portin of fridge to cycle cool air around in box.
The more heated air to escape the vent area the colder the box will be, the freezer will get colder also.